A Blocked Drain — What You Can Try, What You Cannot, and When It Becomes Urgent

A blocked drain is one of the most common plumbing problems in British homes. Most are caused by a slow build-up of grease, hair, soap scum, or food debris — and in many cases, a homeowner can clear a minor blockage without calling anyone. But recurring blockages, foul smells, or water backing up across multiple outlets signal something more serious, and attempting to clear those without professional help can make things considerably worse.

The Difference Between a Blockage and a Build-Up

A slow-draining sink is usually a partial blockage — grease or soap residue narrowing the pipe. A completely blocked drain — water pooling and not draining at all — is a full obstruction. A drain that gurgles when water drains elsewhere in the house suggests a blockage in the shared section of pipework rather than directly below the fixture.

What You Can Safely Try

For a slow-draining sink: remove and clean the trap (the U-shaped pipe under the sink) — this is where grease and debris collect first. A cup plunger creates suction that can shift a partial blockage in the waste pipe. Boiling water poured slowly into a kitchen drain can dissolve a grease build-up. Do not mix chemical drain cleaners with plunging — the caustic residue can splash back and cause chemical burns.

When Not to DIY

Do not attempt to clear a blockage yourself if: water is backing up from multiple outlets (toilet, basin, and shower simultaneously); there is a foul smell from more than one drain; the blockage is in an external inspection chamber or the main sewer line; or you have a septic tank and the drain from it is blocked. These situations require a drainage engineer with CCTV equipment and a high-pressure jetting machine.

Responsibility for Shared Drains

Since October 2011, responsibility for shared sewers (those that serve more than one property) transferred to the water companies. If the blockage is in a shared sewer rather than your private drain, your water company is responsible for clearing it at no charge to you. The boundary is typically the point where your private drain meets the shared sewer — usually at an inspection chamber near your boundary. Your water company can confirm where their responsibility begins.

Fat, Oil, and Grease — the Preventable Cause

Pouring cooking fat down the kitchen drain is the single biggest cause of domestic drain blockages in the UK. Water companies collectively remove around 300,000 sewer blockages per year, many of which are caused by "fatbergs" — accumulations of fat, wet wipes, and other debris. Allowing fat to solidify in a container and disposing of it in the bin costs nothing and prevents most kitchen drain problems.